What is vertex and edge shading?
This feature makes it possible to sharpen or soften individual components of a mesh instead of soften or sharpen the entire mesh. Especially for Low Poly Modeling it can be useful to have more control about the object's appearance and thus to define a more complex shape with less geometry.



Result of sharpen the selected edges only:



Note: In Order to make it work, enable Auto Smooth Option in the Properties Panel > Data. 

When sharpening vertices, the connected edges are also affected:



Render result of sharpen edges only: